In industries which produce liquid products, particularly beverage industries, such as breweries, soft drink bottlers, dairies, etc., large networks of pipes are used to transfer liquid from one place to another. For a variety of reasons, it is necessary to periodically switch the pathways of liquid flow through the pipe network, and accordingly, a large number of switching valves are included in the pipe networks. A modern beverage facility may have a large number of switching valves which are automatically controlled by a central programmable control unit.
A primary requirement in the beverage industry is that cleanliness be maintained throughout the facility. While pipes, through which liquid flows continuously, are generally self-cleaning, it is particularly problematic to maintain cleanliness at the switching valves where liquid may tend to stagnate.
Because it is necessary that the valves, when closed, positively block any liquid flow between pathways, it has become a practice in the industry to use valves with double seats forming leakage chambers therebetween whereby liquid leaking around either seat is drained externally rather than into the other pathway. In order to clean the leakage chambers between the seats of the closed valve, double block and vent or bleed valves have been developed which have passageways through which cleaning solutions may be supplied to the leakage chambers to wash the surfaces thereof. An example of such a valve is described in German Fed. Rep. Published Patent Application No. 2532838.
It is common practice in designing beverage facilities to direct the pipes through a switching area including an array of a large number of switching valves. Double block and vent valves are typically controlled by overhead actuators to which electrical and/or pneumatic control lines are run. When a large number of valves are employed in an array, these lines clutter the area around the valves and may interfere with rapid servicing of the valves. In the valve disclosed in the above-mentioned German Patent Application, overhead cleaning solution lines add to the general clutter above the array of valves. It would be desirable to have double block and vent valves in which the cleaning solution lines are remote from the electrical and pneumatic lines connected to the actuator.